Verizon Wireless customers who use an iPhone 6 or newer can now make voice calls over Wi-Fi, a feature that can improve call quality in areas where the cellular signal is weak. Later this week, Verizon plans to push another free update to late-model iPhones that will enable an HD Voice feature to improve call quality and add other enhancements.

It's free to place calls over Wi-Fi, and unlike Apple's FaceTime video chat, you can call any phone and not just other iPhones. If you're traveling internationally, you can also place free Wi-Fi calls to U.S. numbers, according to GottaBeMobile.com. Wi-Fi calling routes calls over any compatible Wi-Fi network that's in range. Of course, you might have to log into that network for the feature to work.

Verizon plays catchup on Wi-Fi calling for iPhone

Verizon is the last of the four major U.S. carriers to offer Wi-Fi calling on the iPhone. The company said it was waiting for Apple to update its mobile OS to iOS 9.3, which was released on Monday. It's an especially useful feature for making calls when you're far away from cell towers, or when you're inside buildings with structures that interfere with cellular reception.

To use the new feature, you need to upgrade your iPhone to iOS 9.3 — the update is free — and then set up Wi-Fi calling. As soon as you complete the setup process, your calls move automatically from the cellular network to Wi-Fi when it's available.

A number of Verizon Android phones, including recent Samsung Galaxys and Nokia Lumias, have supported Wi-Fi calling for some time.

Verizon HD Voice for iPhone via VoLTE

HD Voice is based on a technology called voice over LTE (VoLTE). Calls made over the 4G LTE network are clearer and less prone to interference, according to Verizon. The tech also enables conference calls with as many as six participants, and it lets users talk and access the Web or download data at the same time. Verizon iPhones running iOS 9.3 should get the VoLTE update on Thursday, March 24, 2016.

Related video: iOS 9.3's best new features

San Francisco journalist Bill Snyder covers business and technology. He writes regularly for CIO.com, Stanford's Graduate School of Business, and the Haas School of Business at the University of California at Berkeley.